Question:
I cant find my NFPA book so I`m sure siemone has the answer to this. Cathedral ceiling about a 60 pitch, 30 feet high at the peak, length about 70 feet. You want to install a beam smoke detector. My memory is a little fuzzy on this, but I believe it has to be about four feet down from the peak to get out of the "dead air space". Boss says put it 1 foot from the peak. Who`s right????

Answer: NFPA 72-1996 5-3.4.6.3 A projected beam-type smoke detector shall be considered equivalent to a row of spot-type smoke detectors for flat and sloped ceiling applications. NFPA 72-1996 5-3.4.7 Peaked. Detectors shall first be spaced and located within 3 ft (0.9 m) of the peak, measured horizontally. The number and spacing of additional detectors, if any, shall be based on the horizontal projection of the ceiling. (See Figure A-5-2.4.4.1.) NFPA 72-1996 A-5-3.4.5.2 On smooth ceilings, a spacing of not more than 60 ft (18.3 m) between projected beams and not more than Ѕ that spacing between a projected beam and a sidewall (wall parallel to the beam travel) should be used as a guide. Other spacing should be determined based on ceiling height, airflow characteristics, and response requirements. In some cases, the light beam projector is mounted on one end wall, with the light beam receiver mounted on the opposite wall. However, it is also permitted to suspend the projector and receiver from the ceiling at a distance from the end walls not exceeding ј the selected spacing. See Figure A-5.3.4.5.2.